Screening, Identification, and Fermentation Condition Optimization of a High-Yield 3-Methylthiopropanol Yeast and Its Aroma-Producing Characteristics

Abstract

A high-yield 3-methylthiopropanol (3-Met) yeast Y1402 was obtained from sesame-flavored Daqu, and it was identified as Saccharomycopsis fibuligera. S. fibuligera Y1402 showed a broad range of growth temperatures and pH, as well as the maximum tolerance to glucose, NaCl, nicotine, and 3-Met at 50% (w/w), 15% (w/v), 1.2 g/L, and 18 g/L, respectively. After optimization using single-factor experiments, a Plackett–Burman design, a steepest ascent test, and a Box–Behnken design, the 3-Met yield reached 4.03 g/L by S. fibuligera Y1402 under the following optimal conditions: glucose concentration of 40 g/L, yeast extract concentration of 0.63 g/L, Tween 80 concentration of 2 g/L, L-methionine concentration of 5 g/L, liquid volume of 25 mL/250 mL, initial pH of 5.3, fermentation temperature of 32 °C, inoculum size of 0.8%, shaking speed of 210 rpm, and fermentation time of 54 h. The fermentation was scaled up to a 3 L fermenter under the optimized conditions, and the yield of 3-Met reached 0.71 g/L. Additionally, an aroma analysis revealed that the flavor substances produced by S. fibuligera Y1402 in sorghum hydrolysate medium was mainly composed of compounds with floral, sweet, creamy, roasted nut, and clove-like aromas. Therefore, S. fibuligera has great potential for application in the brewing of Baijiu and other fermented foods.

Screening of a Saccharomyces cerevisiae Strain with High 3-Methylthio-1-Propanol Yield and Optimization of Its Fermentation Conditions

“…This was verified by experiments conducted under this condition, and the yield of 3-Met was 3.66 g/L, which was close to the predicted value of 3.57 g/L, indicating that the model could predict the optimal conditions for the yield of 3-Met well. The amount of 3-Met produced by S. cerevisiae Y03401 was higher than that reported for H. burtonii YHM-G, but lower than that reported for S. fibuligera Y1402 which was currently the highest reported natural strain for the production of 3-Met [20,21]. In addition, it should be noted that compared with H. burtonii YHM-G, S. cerevisiae Y03401 had relatively weak tolerance to 3-Met, but its yield was higher than that of the former, indicating that there was a certain correlation between the ability of the strain to produce 3-Met and its tolerance to 3-Met, but there was no proportional relationship [21].…”

“…The high-yielding 3-Met yeast strains were identified according to Ma et al, Buchana et al and Dong et al [21,27,28], and their growth temperature range (20,25,30,35,40,45, and 50 • C), pH range (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), glucose tolerance (4.8, 9.1, 13.0, 16.7, 20, 23.1, 25.9, 28.6, 31.0, 33.3, 35.5, 37.5, 39.4, 41.2, 42.9, 44.4, 45.9, 47.4, 48.7, and 50.0%, w/w), NaCl tolerance (0, 3,6,8,11,13,15,17,19, and 21%, w/v), ethanol tolerance (0, 3, 6, 9, 12, 15, 18, and 21%, v/v), and 3-Met tolerance (1,2,3,4,5,6,7,8,9,10,11,12,13,14, and 15 g/L) were determined using liquid culture methods. The cell density after 36 h of culture was measured using turbidity, and the absorbance values at 560 nm of different samples were determined with the c...…”

“…The lack or almost complete absence of critical strains that generated significant amounts of 3-Met during the brewing process was one of the main causes of the aforementioned process. In reported studies, except for Kluyveromyces lactis KL71, Hyphopichia burtonii YHM-G, S. cerevisiae SC408, S. cerevisiae SC57, S. cerevisiae S288C and Saccharomycopsis fibuligera Y1402, other natural strains produced less than 0.5 g/L of 3-Met under optimal fermentation conditions [13][14][15][16][17][18][19][20][21]. Modern genetic technology and genetic modification have made it entirely possible to increase natural strains' capacity to produce high levels of 3-Met; however, Chinese laws and regulations currently prohibit the use of genetically modified strains in the production of traditional brewing food, which raises concerns among consumers regarding the safety of brewing food [22][23][24].…”

“…Currently, multiple yeast strains that produced 3-Met had been screened from the brewing environment of traditional brewing foods, such as S. cerevisiae [25], Zygosaccharomyces rouxii [1], K. lactis [16], Geotrichum candidum [26], H. burtonii [21] and S. fibuligera [20]. However, except for H. burtonii and S. fibuligera, which had a higher ability to produce 3-Met, the levels of 3-Met produced by other strains were generally low, which cannot meet the needs of products for 3-Met content.…”

Optimization of High-Density Fermentation Conditions for Saccharomycopsis fibuligera Y1402 through Response Surface Analysis

“…In our previous work, we isolated a yeast strain of S. fibuligera Y1402 from the environment of Baijiu (Chinese liquor) production. This strain demonstrated high production of flavor compounds such as 3-methylthiopropanol and phenylethanol [25]. It significantly improved the quality of tobacco products when applied to tobacco leaf fermentation (related research is still pending publication).…”